This patent document relates to signal filtering and filtering devices including signal filtering based on multiple-pole filters.
Signal filters with multiple poles can be used to achieve steep roll-off at the edge of the transmission band of the filters. Steep roll-off in signal filters is desirable in various applications. The number of poles of a filter can be designed to be high in order to achieve a certain level of steepness of the roll-off. In RF circuits, an RF filter based on electronic circuit elements require a large number of inductors and capacitors to achieve a large number of poles. Therefore, an RF filter with a steep roll-off can be a complex and large in structure and can be expensive. In optical devices or systems, optical filters with multiple poles can be constructed by coupling multiple optical filters to one another. A large number of optical filters can be coupled to form a composite optical filter with a large number of poles in the filter transfer function of the composite filter.